Frequency multiplier



Dec. 1, 1942. A. L. NELSON 2,303,575

FREQUENCY MULTIPLIER Filed April 29, 1940 FIG.| 3 l2 FIG.2

TIME CURRENT INVENTOR ATTORNEY.

Patented Dec. 1, 1942 FREQUENCY MULTIPLIER Arthur L. Nelson, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application \April 29, 1940, Serial No. 332,299

7 Claims.

This invention relates to frequency multipliers, and particularly to means for tripling high and ultra-high frequencies.

Frequency multiplier arrangements of the prior art have generally operated by utilizing the non-linear relation which exists between the grid voltage and plate current, or the non-linear relation between the grid voltage and gridv current, of a vacuum tube to produce harmonics of the impressed signal. The output currents in such arrangements include components of the desired frequency or frequencies which are se lected by suitable means, such as sharply tuned filters. Such methods of frequency multiplication are inherently inefficient, complicated and expensive and moreover are incapable of providing output signals of substantially the same wave form as that of the impressed signal.

The present invention is directed to the solution of the problem of providing frequency mul- Z tiplication without the disadvantages of arrangements for this purpose heretofore provided.

The primary object of the present invention,

therefore, is to provide an improved method of and means for effecting frequency multiplication characterized by simplicity and high efiiciency.

In accordance with the present invention, there is provided a frequency multiplier which comprises first and second signal repeating means adapted to repeat relativelylarge portions and relatively small portions, respectively, of a signal impressed thereon. An output circuit for the repeating means is provided which combines the repeated signal portions in opposite phase to provide an output signal having an integral number of times the frequency of the input signal.

, In one approved embodiment of the invention, the frequency multiplier comprises two pairs of similar multi-element vacuum tubes. The vacuum tubesof one pair are biased substantially to cut-ofi, and the vacuum tubes of the second pair are biased'to several times cutoff. A portion of the voltage which is developed across a resonant circuit tuned to the frequency of the input signal is-applied between the control electrodes of the first pair of vacuum tubes, and the total voltage developed across theinput resonant circuit is applied between the controlelectrodes of the second pair. The output circuit includes a resonant circuit which is tuned to three times the frequency of the inputsignal. Thejterminals of this resonant circuit are connected' directly to the output electrodes of one pair of vacuum tubes, and with a reversed connection to the output electrodes of the other pair.

For a better understanding of the invention together with the other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is a schematic circuit diagram of a frequency multiplier in-accordance with the present invention; and Fig. 2' is a graph representing certain operating characteristics of the device of Fig. 1.

Referring now more particularly to Fig. 1 of the drawing, there is shown schematically a frequency tripler embodying the present invention in a preferred form. In general, the frequency tripler includes vacuum tubes I, 2, 3 and 4'which are substantially identical. Each of tubes I, 2, 3, 4 has a cathode 5 which may be of either the filament or indirect-heater type. Conventional means may be employed for heating oath-odes 5, these means not being shown in the drawing to avoid unnecessary complication thereof. Tubes I, 2, 3 and 4 also respectively include grids 6, I, B and 9 which are substantially identical, but which are designated by different reference numerals for convenience in describing the operation of the system. Anodes III, II, I2 and I3 are provided for the tubes I, 2, 3 and 4, respectively, and are also substantially identical but are designated by different reference numerals for convenience.

Cathodes '5 of vacuum tubes I and 2 are grounded through battery I4 connected with-the polarity indicated in the drawing. Cathodes 5 of vacuum tubes 3 and 4 are connected to the positive terminal of battery I4thr0ugh battery I5 which has the polarity indicated in the draw- A parallel resonant circuit comprising an inductance element I6 and'a condenser I1 is connected between grids 8 and 9 of vacuum tubes 3 and 4. Condenser I is preferably adjustable. The center tap I8 of-inductor IB is grounded. Grids 6 and l of vacuum tubes I and2 areconnected, respectively, to taps I9 and 20 of inductor I6. An input Winding 2I is coupled to inductor I6 and connected'to input terminals 22 and 23.

A parallel resonant circuit comprising an inductance element 24 and a condenser 25 isco11- nectedbetween anodes I2 and I3 of vacuum tubes 3 and 4 and, with a reversed connection, between anodes ID and II of vacuum tubes I and 2. Condenser 25 is preferably adjustable. Center tap 26 of inductance element 24 is grounded through anode-supply battery 21, having the polarity indicated in the drawing. An output winding 28 is coupled to inductance element 24 and connected to output terminals 29 and 30.

The signal to be multiplied is applied to input terminals 22 and 23, and its frequency is designated in the drawing as ft. The output signal appears across output terminal 29 and 30, its frequency being designated in the drawing by is.

The voltage of battery I4 is such that vacuum tubes I and 2 are biased substantially to cutoff, and the combined voltage of batteries I4 and I5 in series is such that vacuum tubes 3 and 4 are biased to several times cut-off. Resonant circuit IB-Il is tuned to the frequency ii of the input signal, and resonant circuit 24-25 is tuned M to the frequency is of the output signal.

The operation of the device of Fig. 1 may be readily understood by reference to the curves of Fig. 2. These curves are all plotted to the same time base, with the time increasing to the right, k

as indicated. Curve I1 indicates the anode current of vacuum tube I which flows through inductance element 24 during the positive halfcycle swing of input signal voltage applied to grid 6 of this tube. Curve 12 indicates the corresponding anode current of vacuum tube 2 during the half-cycle positive swing of th input signal voltage applied to its grid 1. It will be understood that, since vacuum tubes I and 2 are biased substantially to cut-off, anode current flows in each tube during only a half-cycle period of the input signal, and that, since the grids of the tubes are in phase opposition, when current is flowing in the anode circuit of one tube it is not flowing in the anode circuit of the other tube.

Curve I3 indicates the anode current of vacuum tube 3 which flows through inductance element 24. Since this tube is biased by a voltage several times the bias voltage necessary for cut-off, anode current flows only during a relatively small portion of the positive half-cycle of input signal voltage applied to its grid 8. Although the voltage applied to grid 8 of vacuum tube 3 is in phase with the voltage applied to grid 6 of vacuum tube I,

the respective anode currents of these tubes through inductance element 24 are in phase opposition due to the reversed connections between resonant circuit 24-25 and vacuum tubes I and 2. Curve I4 indicates the corresponding anode current of vacuum tube 4. The voltage applied to grid 9 of Vacuum tube 4 is in phase opposition to that applied to grid 8 of vacuum tube 3, and therefore the current represented by curve I4 flows in the opposite direction through inductance element 24 from that represented by the curve I3.

Curve IR represents the circulating current which flows in resonant circuit 24-25, and hence corresponds with the output signal of the tripler. It will be noted that the current represented by curve IP. has three times the frequency of the current represented by curve I1 and I2, which in turn corresponds in frequency with the input signal voltage.

In operation, a voltage of frequency I1 is applied to input terminals 22 and 23 from any suitable source of excitation. Let it be assumed that, at a given instant, grid -6 of vacuum tube I is at the peak of its positive half-cycle. A resulting current flows in the anode circuit of tube I, its peak value being indicated by the point 3| of curve I1. At the same instant, a voltage of the same phase but of greater amplitude is applied to grid 8 of vacuum tube 3, causing a current to flow in the anode circuit of tube 3, the amplitude of which is indicated by the point 32 of curve I3. Due to the reversal of connections mentioned above, the anode current of tube 3 flows through inductance element 24 in a direction opposite to that in which the anode current of tube I flows. The flow of currents I1 and I: through inductance element 24 causes the flow of a circulating current in resonant circuit 24-25 which is substantially equivalent to the resultant of currents I1 and I3 were they to be algebraically added, but the wave form of the circulating current is somewhat altered by the fly-wheel effect of resonant circuit 24-25 so that it closely approaches the sinusoidal wave form graphically represented in Fig. 2 by curve IR. Since the negative peak value of the anode current of vacuum tube 3 occurs at the same instant as the maximum positive value of the anode current of vacuum tube I, the resultant current indicated by curve IR has three peaks for each single peak of the individual component currents, and hence the output current has three times the frequency of the current due to the input voltage. Vacuum tubes 2 and 4 function, respectively, in the same manner as vacuum tubes I and 3, except in the opposite phase, over the second half-cycle of the input signal voltage wave. The voltage induced in winding 28 and appearing between output terminals 29 and 30, therefore, has three times the frequency of the voltage impressed upon input terminals 22 and 23.

It will be understood that the relative amplitudes of the positive and negative swings of the resultant current In depend upon the amplitudes, respectively, of currents I1 and I: (or of I4 and I2), and that the amplitudes of the individual anode currents in turn depend upon the signal voltage applied to grids 6 and 1 of vacuum tubes I and 2, compared with the signal voltage applied to grids 8 and 9 of vacuum tubes 3 and 4. Taps I9 and 20, therefore, are so positioned on inductor I6 that the positive and negative swings of the resultant current In are substantially equal.

It will be understood that vacuum tubes I, 2, 3 and 4 of Fig. 1 may be replaced by a single pair of double triodes without departing from the scope of the present invention. If vacuum tubes I and 2 are replaced by a single double triode, and vacuum tubes 3 and 4 by a similar second tube, the double triodes may be of the type having a single cathode common to the two triode sections. If, however, vacuum tubes I and 3 are replaced by a single double triode, and vacuum tubes 2 and 4 by a second double triode, then the double triodes must be of the type wherein a 1separate cathode is provided for each triode secion.

The frequency ranges in which the device of the present invention may be used are limited principally by the interelectrode capacitances of the vacuum tubes employed. No neutralization means are necessary for the stable operation of the device of the present invention. Experiments prove that the new device is practical and admirably suited for multiplying input signals having frequencies up to the order of 100 megacycles.

Whereas previous frequency multipliers of the grid-distortion type required an extremely high driving power and had anode-circuit efliciencies of only 20 to 30 percent, the device of the present invention requires relatively small driving power and has a relatively high anode-circuit efficiency. This high eiiiciency is due to the fact that, whereas vacuum tubes l and 2 operate as ordinary class B amplifiers, Vacuum tubes 3 and 4 operate as class C amplifiers under even more favorable conditions due to their smaller operating angle. Still greater efliciency may be realized by operating all four of the tubes in the class C region.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A frequency multiplier comprising an input circuit adapted to have an input signal impressed thereon, first signal repeating means connected to said input circuit and adapted to repeat relatively large portions of said input signal, second signal repeating means connected to said input circuit and adapted to repeat relatively small portions of said input signal, and an output circuit for said repeating means for combining said repeated signal portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal.

2. A frequency multiplier comprising an input circuit adapted to have an input signal impressed thereon, means for producing a small-amplitude signal and a large-amplitude signal corresponding in frequency to said input signal, first signal repeating means adapted to repeat relatively large portions of said small-amplitude signal,

second signal repeating means adapted to repeat relatively small portions of said large-amplitude signal, and an output circuit for said repeating means for combining said repeated signal portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal.

3. A frequency multiplier comprising an input circuit adapted to have an input signal impressed thereon, means for producing a small-amplitude signal and a large-amplitude signal corresponding in frequency to said input signal, first signal repeating means adapted to repeat substantially half-cycle portions of said small-amplitude signal, second signal repeating means adapted to repeat substantially smaller portions of said large-amplitude signal, and an output circuit for said repeating means for combining said repeated signal portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal.

4. A frequency multiplier comprising an input circuit adapted to have an input signal impressed thereon, means for producing a small-amplitude signal and a large-amplitude signal corresponding in frequency to said input signal, first signal repeating means adapted to repeat relatively large portions of said small-amplitude signal, second signal repeating means adapted to repeat relatively small portions of said large-amplitude signal, and an output circuit for said repeating means for combining said repeated signal portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal, said firstmentioned means being so proportioned that the relative amplitudes of said small-amplitude and large-amplitude signals are such that the positive and negative swings of said output signal are substantially equal.

5. A frequency multiplier comprising an input circuit adapted to have an input signal impressed thereon, a first pair of amplifying vacuum tubes connected to said input circuit and so biased as to repeat relatively large portions of said input signal, a second pair of amplifying vacuum tubes connected to said input circuit and so biased as to repeat relatively small portions of said input signal, and an output circuit for said amplifying vacuum tubes for combining said repeated signal portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal.

6. The method of multiplying the frequency of an alternating-current input signal which comprises the steps of repeating relatively large portions of said input signal, repeating relatively small portions of said input signal, and combining said repeated portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal.

7. The method of multiplying the frequency of an alternating-current input signal which comprises the steps of producing a small-amplitude signal and a large-amplitude signal corresponding in frequency to said input signal, repeating relatively large portions of said small-amplitude signal, repeating relatively small portions of said large-amplitude signal, and combining said repeated portions in opposite phase to produce an output signal having a frequency which is a multiple of the frequency of said input signal,

ARTHUR L. NELSON. 

